The field of the invention relates to control systems for maintaining engine air/fuel operation in response to an exhaust gas oxygen sensor. In a particular aspect, the field further relates to correcting the EGO sensor output.
Air/fuel ratio feedback control systems responsive to exhaust gas oxygen sensors are well known. The sensor output is typically compared to a reference value selected at the approximate midpoint in expected peak-to-peak excursion of the sensor output. Ideally, a two-state signal is thereby generated which indicates when engine air/fuel operation is either rich or lean of a predetermined air/fuel ratio such as stoichiometry. In an attempt to compensate for fluctuations in the sensor output due to deterioration or low temperature, an approach was disclosed in U.S. Pat. No. 4,170,965 to time average the sensor output through an RC filter, and use the time averaged value as the reference value.
The inventors herein have recognized several problems with the above approach. Using a time averaged output of the EGO sensor as the comparison reference will not always result in alignment of the reference with the midpoint in peak-to-peak excursion of the EGO sensor output. For example, when the sensor output is asymmetrical, or the sensor output is at other than a fifty percent duty cycle, the reference voltage will not be in alignment with the midpoint of the peak-to-peak sensor output. The switch point in the two-state signal may therefore not be in perfect alignment with the peak efficiency operating window of the catalytic converter.